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ELECTROCARDIOGRAM

How Procedure is performed 

The individual lies on a bed or couch while electrodes are placed on the skin at thewrists, ankles, and several locations across the chest. The electrodes are connected by

wires to a control unit that selects different combinations of heart signals to record. The

resulting electrical signals are amplified and recorded on paper or displayed on a

monitor. The test takes only a few minutes and is painless.

Definition:

Is the graphical recording of the electrical activities of the heart. It indicates alteration

of myocardial oxygenation.

Purpose:

To diagnose electrical aberrations in the electrical activity of the heart, such as:

a. MI, Angina Pectoris

b. Cardiac dysrythmias

c. Cardiomegaly

d. Inflammatory disease of the heart

Principles:

1. Place leads properly to get accurate results/ reading

2. Explain the procedure to the patient.

3. Provide privacy

Electrocardiogram taking

1. Explain the procedure to the patient

2. Assemble the equipments:

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- ECG machine

- Electrode paste

- Conductive paste or alcohol swab

3. Close room/door/ bedside curtain

4. Place the client in a supine position or semi-fowlers position

5. Remove clothing on the chest part

6. Instruct client to lie still without talking

7. Standardize ECG machine

8. Cleanse and prepare the skin, wipe the site with alcohol

9. Attach leads:

Limb leads:

Right arm: RED

Left arm: yellow

Right leg: black

Left leg: green

PRECORDIAL LEADS:

V1- Right 4th intercostals space sternal border RED

V2- Left 4th intercostals space sternal border YELLOW

V3- midway, between V2 and V4 left GREEN

V4- 5th intercostal space, mid clavicular left BROWN

V5- 5th intercostals space anterior axillary left BLACK

V6- 5th intercostals space, midaxillary left VIOLET

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For 15 lead ECG in addition to 12 leads

V3- Right intercostals space at level of V3

V4- Right intercostals space mid clavicular 

V7-5th Intercostals space postertior left

10. Start to run the ECG machine, 12 lead and long lead 11

Bipolar limb leads: L1, L2, and L3

Unipolar limb leads: AVR, AVL, and AVF

Chest leads: V1, V2, V3, V4, V5, and V6

11. Disconnect electrodes and leads and wipe electrode paste if present.

12. On the ECG strip, check the tracing and write the name of the patient, age, date and time

taken

13. Mount the ECG strips on the ECG sheet

14. Refer the ECG results to the doctor 

15. Return ECG machine properly

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The 12-lead ECG

Over the years, we have evolved several systems that go to make up the 12-lead ECG. These are:

• Bipolar leads: the reference point is on one limb, the `sensing' electrode (if you wish) is

on another limb. The leads are termed I, II, and III.

• Unipolar leads: The reference point is several leads joined together, and the sensing lead

is on one limb. These leads are conventionally augmented , in that the reference lead on

the limb being sensed is disconnected from the other two.

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• The V leads, which extend across the precordium, V1 in the fourth right interspace, V2

4th left, V4 at the apex (5th interspace, midclavicular line), V3 halfway in between V2

and V4, and V5 & V6 in the 5th interspace at the anterior and mid axillary linesrespectively.

We can visualise the directions of the various leads --- I points left, and aVF points directly down(in a 'Southward' direction). The other leads are arranged around the points of the compass ---

aVL about 30o more north of I, II down towards the left foot, about 60 o south of I, and III off to

the right of aVF. aVR `looks' at the heart from up and right, so effectively it's seeing thechambers of the heart, and most deflections in that lead are negative.

(a net positive vector in AVR is unusual, and suggests that lead placement was incorrect. If the

leads were correctly sited, then think dextrocardia, or some other strange congenital

abnormality).

It's usual to group the leads according to which part of the left ventricle (LV) they look at. AVLand I, as well as V5 and V6 are lateral, while II, III and AVF are inferior . V1 through V4 tend to

look at the anterior aspect of the LV (some refer to V1 and V2 `septal', but a better name is

 perhaps the `right orientated leads'). Changes in depolarisation in the posterior aspect of the heartare not directly seen in any of the conventional leads, although "mirror image" changes will tend

to be picked up in V1 and V2.

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ECG READING

An ECG Paper 

Waves and Intervals

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Feature Description Duration

RRinterval

The interval between an R wave and the next R wave is the inverse of the heartrate. Normal resting heart rate is between 50 and 100 bpm

0.6 to 1.2s

P waveDuring normal atrial depolarization, the main electrical vector is directed fromthe SA node towards the AV node, and spreads from the right atrium to theleft atrium. This turns into the P wave on the ECG.

80ms

PRinterval

The PR interval is measured from the beginning of the P wave to the beginningof the QRS complex. The PR interval reflects the time the electrical impulsetakes to travel from the sinus node through the AV node and entering theventricles. The PR interval is therefore a good estimate of AV node function.

120 to 200ms

PRsegment

The PR segment connects the P wave and the QRS complex. This coincideswith the electrical conduction from the AV node to the bundle of His to thebundle branches and then to the Purkinje Fibers. This electrical activity doesnot produce a contraction directly and is merely traveling down towards theventricles and this shows up flat on the ECG. The PR interval is more clinicallyrelevant.

50 to 120ms

QRScomplex

The QRS complex reflects the rapid depolarization of the right and leftventricles. They have a large muscle mass compared to the atria and so theQRS complex usually has a much larger amplitude than the P-wave.

80 to 120ms

J-pointThe point at which the QRS complex finishes and the ST segment begins. Usedto measure the degree of ST elevation or depression present.

N/A

STsegment

The ST segment connects the QRS complex and the T wave. The ST segmentrepresents the period when the ventricles are depolarized. It is isoelectric.

80 to 120ms

T wave

The T wave represents the repolarization (or recovery) of the ventricles. Theinterval from the beginning of the QRS complex to the apex of the T wave isreferred to as the absolute refractory period . The last half of the T wave isreferred to as therelative refractory period (or vulnerable period).

160ms

ST The ST interval is measured from the J point to the end of the T wave. 320ms

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interval

QTinterval

The QT interval is measured from the beginning of the QRS complex to the endof the T wave. A prolonged QT interval is a risk factor for ventricular tachyarrhythmias and sudden death. It varies with heart rate and for clinicalrelevance requires a correction for this, giving the QTc.

300 to

430ms[citation

needed ]

U waveThe U wave is not always seen. It is typically low amplitude, and, by definition,follows the T wave.

J waveThe J wave, elevated J-Point or Osborn Wave appears as a late delta wavefollowing the QRS or as a small secondary R wave . It is consideredpathognomic of hypothermia or hypocalcemia.[24]

Interpreting an ECG

Interpreting an electrocardiogram (ECG) is a skill you can master only with practice. The

three basic elements of an ECG waveform are the P wave, the QRS complex, and the T

wave. Use these elements to develop a consistent approach for reading waveforms,

following this eight-step approach.

1. Evaluate the P wave.

Observe its size, shape, and location in the waveform. If the P wave consistently

proceeds the QRS complex, the electrical impulse is being initiated bv the sinoatrial

node.

2. Evaluate the atrial rhythm.

The P wave should occur at regular intervals, with only small variations associated with

respiration. Using calipers, you can easily measure and compare the interval between P

waves (the P-P interval).

3. Determine the atrial rate.

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A quick method is to count the number of P waves in two 3-second segments and

multiply by 10. For a more accurate approach, count the small squares between the

apex of two P waves. Each small square equals 0.04 second; 1,500 squares equal 1

minute. Divide 1,500 by the number of squares you counted to get the atrial rate.

4. Calculate the duration of the PR interval.

Count the small squares between the beginning of the P wave and the beginning of the

QRS complex. Multiply that number by 0.04 second.The normal interval is between 0.12

and 0.20 second, or between three and five small squares wide. If the interval is wider,

the conduction of the impulse to the ventricle is delayed.

5. Evaluate the ventricular rhythm.

Use calipers to measure the R-R intervals. Place the calipers on the same point of each

QRS complex. If the R-R intervals are consistent, the ventricular rhythm is regular.

6. Determine the ventricular rate.

Use the formula for calculating the atrial rate (Step 3), except count the small squares

between two R waves. Also check that the QRS complex is shaped appropriately for the

lead you're monitoring.

7. Calculate the duration of the QRS complex.

Count the squares between the beginning and the end of the QRS complex and multiply

by 0.04 second. A normal QRS complex is less than 0.72 second.

8. Calculate the duration of the QT interval.

Count the number of squares from the beginning of the QRS complex to the end of the

T wave. Multiply this number by 0.04 second. The normal range is 0.36 to 0.44 second,

or 9 to 11 small squares.